METHODS USED FOR CATARACT EVALUATION: DOCUMENTATION OF CATARACT AND ITS EFFECT ON VISIONREFERENCES

Careful evaluation of the lens is an essential part of a complete eye examination. Cataracts (Figs. 1, 2, 3, 4), in particular age-related or senile cataracts, are among the most common ocular finding in older patients and accounts for up to 50% of blindness worldwide.1-3 In the United States, among Medicare beneficiaries, cataract is the most common condition for which eye care services are sought, accounting for 45% of visits to eye doctors.4 In addition, cataract surgery is the most frequently performed surgical procedure among 30 million Medicare beneficiaries.4 With the prolongation of human life by advances in medicine, increasing numbers of patients with age-related disorders, especially cataracts, are to be expected.

Fig. 1. Cortical cataract using (A) direct illumination (B) retroillumination. Cortical cataracts usually start in the lens periphery and encroach into the visual axis (and interfere with central vision) only in later stages.

HYPERLINK "http://www.eyecalcs.com/DWAN/pages/v1/ch073b/002f.html" \t "_blank" Fig. 2. Brunescent (brown) nuclear cataract using (A) narrow beam slit illumination and (B) retroillumination. The cataract is best seen by direct slit illumination. In retroillumination, as seen in this image, the outline of the nuclear cataract may be seen due to its increased refractive index, although the cataract does not cast any shadows. Because of its central location, this cataract may cause distortion of images early in their development.

HYPERLINK "http://www.eyecalcs.com/DWAN/pages/v1/ch073b/003f.html" \t "_blank" Fig. 3. Posterior subcapsular cataract (PSC) using (A) direct illumination and (B) retroillumination. PSCs usually start centrally and extend toward the periphery. For this reason, they interfere with visual function, causing glare disability early.

Fig. 4. Mixed cortical-nuclear-posterior subcapsular cataract.

The primary purpose in managing a patient with cataract, as stated in the American Academy of Ophthalmology's, Preferred Practice Pattern for Cataract in the Adult Eye,5 is to improve functional vision and the quality of life. Currently, the only effective treatment of cataract is surgical removal with, in most cases, insertion of an intraocular lens. The indications for surgery are: when the cataract-impaired vision no longer meets the patient's needs, and the anticipated benefits of surgery outweigh the risks. No single test adequately describes the effect of cataract on a patient's visual status or functional ability.5 It is important then, that each clinician be well versed in the current techniques of cataract assessment (such as cataract detection, documentation, and monitoring methods), and the assessment of the total effect of the cataract on the patient's daily needs and quality of life (such as visual function and functional impairment tests).

Noncataractous lens changes occur with normal aging6,7 and the clinical difference between early cataract and age-related change is often not clear-cut. The difference becomes more obvious as the cataract progresses, hence the need for regular follow-up examinations in the elderly. Most clinicians tend to vary in their subjective grading of cataractous changes. For this purpose, newly developed clinical cataract grading systems (see below) using standard cataract photographs help clinicians to document the progress of cataracts better and to compare their assessment with that of other clinicians. These grading systems are especially useful in clinical research studies as well as for publication of clinical reports.

Once a cataract is diagnosed, the clinician should determine its overall effect on visual function and the well-being of the patient. These assessments will serve as the basis for a decision whether to recommend any treatment such as cataract surgery. A careful inquiry should be made into the patient's daily, occupational, leisure, and social activities and document any cataract-related impairment. The recent introduction of functional disability measures, such as the NEI VFQ-25 and VFQ-14 tests (see below), allow more objective and accurate measures of the functional disability caused by a cataract on a particular patient.

This chapter aims to summarize currently available methods for the evaluation of cataracts for clinicians and to describe new promising methods being developed and tested. Tremendous technological advances in the field of computers, photography, and imaging in the last 10 years have revolutionized ophthalmology, especially in the diagnosis and treatment of eye disorders including cataracts. Developments in recent years have helped standardize various methods used for the documentation and monitoring of cataracts as well as the documenting the effect of cataracts on a patient's visual function and quality of life. Table 1 gives a list of these methods, which are then discussed in detail in the text.

Table 1. Methods used in Cataract Evaluation: Documentation of Cataract and Its Effects on Vision

A. Visual acuity/function tests

1. Snellen/ETDRS acuity charts or projectors

2. Glare and contrast sensitivity tests

3. Potential acuity tests

a. Pinhole Aperture

b. Entoptic Phenomenon

c. Macular function tests: Potential Acuity Meter (PAM), clinical interferometers

4. Tests for refractive distortions in the lens: Resolution test target projection ophthalmoscope (acuityscope, Oqual)

B. Functional Impairment/Quality-of life tests

1. NEI VFQ25

2. VF14

3. Others: Short Form 36 (SF-36), Activities of Daily Vision (ADV), Sickness Impact Profile

C. Clinical examination and documentation of physical lens changes

1. Clinical examination with hand-held light, slit-lamp biomicroscopy and ophthalmoscopy; and accessory devices

2. Standardized clinical grading and photographic systems (comparing a patient's cataract with standard photographs)

a. Lens Opacities Classification System (LOCS) III Clinical and Photographic Grading system

b. Wisconsin Clinical and Photographic Cataract Grading system

c. Wilmer Clinical and Photographic Cataract Grading system

d. Oxford Clinical Cataract Grading system

e. Age-Related Eye Disease Study (AREDS) Cataract Grading System

f. Other systems such as the Japanese CCRG Cataract Grading system and the World Health Organization Cataract Grading System

3. Specialized slit-lamp photography/imaging

a. Scheimpflug slit lamp imaging and densitometry systems

b. Retroillumination imaging and area analysis systems

c. Others: Laser slit lamp, sequential color imaging and analysis

D. New methods under development:

1. Quasielastic or dynamic light scattering (QELS or DLS)

2. Magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) spectroscopy

3. Wavefront technology

4. Raman spectroscopy

5. Autofluorescence

6. Optical coherence tomography

Back to TopMETHODS USED FOR CATARACT EVALUATION: DOCUMENTATION OF CATARACT AND ITS EFFECT ON VISION

VISUAL ACUITY TESTING

Snellen Charts and Projectors

Since its introduction in 1862, the Snellen test chart has been the clinically preferred standard used to measure visual acuity, and thus also used initially to assess the effect of cataracts on visual function. It remains the gold standard used to measure minimum separable and legible acuity,8 to measure the effect of any abnormal state of the eye, as well as for measurement of the effectiveness of medical and surgical intervention in diseased states of the eye.

Recently, the need to be able to obtain measurements of visual acuity values that can be used for statistical analysis for research studies has led to further standardization and modifications of the Snellen chart. One such modification for such purposes is the Early Treatment Diabetic Retinopathy Study or ETDRS version.9 It was designed to have a geometric progression of the letter size of test letters and standardized lighting of the chart. Visual acuity scores are expressed as the logarithm of the minimal angle of resolution (LogMar), which is linear, meaning, it decreases by 0.1 unit for each lower line on the chart. Most current clinical eye research studies use the ETDRS visual acuity chart measurements as a major end point.

As recently as four decades ago, as a result of high complication rates, cataract surgery was deferred until a patient did not have much to lose in terms of visual acuity, should intraoperative or postoperative surgical complications occur. Patients were advised to wait until their cataract was ripe and their Snellen visual acuity dropped down to 20/80 or worse before contemplating surgery. With the development of safer techniques such as the intracapsular cataract extraction (ICCE) technique using the Cryoprobe, and later the extracapsular cataract extraction (ECCE) technique using automated irrigation-aspiration (I/A) devices and implantation of an intraocular lens (IOL), the indication for cataract surgery was lowered to a Snellen acuity of 20/40 or worse coupled with anticipated improvement of vision. In most states, a minimum requirement for an unrestricted license to drive a vehicle was a visual acuity of 20/40 and a patient could potentially lose his/her driver's license should his/her Snellen acuity drop below this level. Hence, the cataract needed to be removed to allow the patient to continue driving.

Currently, with the development of even safer techniques such as phacoemulsification followed by implantation of an IOL (resulting in lower complication rates and superb postoperative vision), the indications for surgery have further changed. The American Academy of Ophthalmology (AAO)'s Preferred Practice Pattern for Cataract in the Adult Eye states that there is no single test that adequately describes the effect of cataract on visual status and functional ability. Cataract/IOL surgery is therefore indicated when the vision no longer meets the requirements of the patient, and when the expected surgical benefits outweigh the risks. Hence, not only the level of visual acuity but other considerations such as the ability to perform daily tasks of living, ability to perform work or avocations, and good quality of life in general are equally important in deciding when cataract extraction should be performed.

Snellen-type visual acuity tests measure the eye's ability to resolve fine detail at high contrast but do not adequately describe the ability to see large but low contrast patterns such as faces or nearby objects. A cataract may affect the results of the Snellen acuity test minimally, and yet a patient may already experience difficulties in daily activities such as driving or walking especially in bright sunlight or at night, or have difficulty in their line of work, such as lawyers or accountants who need to read fine print accurately or architects who need to see fine lines in a line drawing.

Recently, a number of tests have been proposed to document changes in visual function that are not detected by the Snellen visual acuity test. Among the important ones are contrast sensitivity testing and glare testing.10 A number of glare and contrast sensitivity tests have been devised and continue to be further refined, especially with the use of computer monitors. Potential acuity tests such as the Guyton-Minkowsky Potential Acuity Meter (PAM) and clinical interferometers are used mainly to determine macular function independent of media opacities such as corneal, lens, and vitreous opacities. The Resolution Test Target Projection Ophthalmoscope was developed to document distortions in vision that are not adequately determined by the Snellen acuity test. The following are discussions of each of these.

Clinical Contrast Sensitivity Tests

Contrast sensitivity is a measure of the amount of contrast required to detect or recognize the target. Cataracts increase intraocular light scatter causing a reduction in retinal image contrast, and a subsequent decrease in contrast sensitivity. In general there are two types of devices used for contrast sensitivity testing.10 The traditional devices consist of sine wave gratings, which are patterns of alternating light and dark bars produced and controlled by computers, wherein the spatial frequency, contrast luminance, field size, and attenuation at the edge of the field are either modifiable or fixed.11 Examples of this are, among others, Optec 3500 Vision Tester (Stereo Optical Co., Inc., Chicago, IL), B-VAT PC system (Medtronic Solan Co., Inc., Jacksonville, FL), Smart System 20/20 (M & S Technologies, Inc., Chicago, IL), and CSV-1000E Contrast Sensitivity Instrument (VectorVision, Inc., Arcanum, OH). The second type of devices are based on photographically reproduced sine wave gratings (such as the Arden plates and the Vistech vision contrast test system) or variable contrast optic types (such as the Regan letter chart, the Vistest picture test, the Pelli-Robson letter chart, and the Melbourne edge test),12Hess and Woo13 first reported contrast sensitivity function loss in patients with cataracts. They suggested that early cataracts cause high-spatial frequency loss, whereas more advanced cataracts produce both high- and low-spatial frequency losses. Drews-Bankiewicz et al.14 documented correlations between early nuclear cataracts with loss of contrast sensitivity in the intermediate and high spatial frequencies (4 to 16 cycles per degree). Lasa et al.15 found significant contrast sensitivity loss only in advanced cortical and posterior subcapsular cataracts. This loss was also correlated with decreased Snellen visual acuity. Adamsons et al.16 however, found that contrast sensitivity scores were lower for all patients with lens opacities than for clear lenses at high frequencies only, and all lens opacity groups scored similarly with each other. Recently, Kuroda et al.17 found a significant correlation between increasing lens density (using the Scheimpflug camera to measure lens density) and loss of contrast sensitivity in nuclear and cortical cataracts at 12 cycles per degree.

Glare Testing

Glare sensitivity refers to the change in visual function caused by the presence of a glare (light) source in another part of the visual field. In general, glare can be divided into either discomfort or disability glare. Discomfort glare causes a photophobic sensation without measurable effects on visual function, whereas disability glare causes reduction in visual function because of the presence of a bright light source.18 Disability glare is a specific type of glare caused by light scattered by the ocular media and is the type of glare that is commonly tested by the devices that have been developed to document glare.

Glare testing is helpful in documenting glare disability especially for those patients who complain of glare when driving at night and having difficulty with oncoming headlights, or having difficulty reading road signs when there is bright sunlight.19 Examples of these devices include the Brightness Acuity Tester or BAT (Marco Ophthalmics, Jacksonville, FL), the CSV 1000HGT (VectorVision Inc., Arcanum, OH), and the Optec 3500 Vision tester (Stereo Optical Co., Inc, Chicago, IL).

Potential Acuity Tests

Pinhole acuity8 is easy and quick to perform and is often used when visual acuity is less than 20/20. It can give useful information, especially if one obtains a good reading. However, a poor pinhole acuity result does not necessarily mean poor macular function because the decrease in retinal illumination produced by use of the small aperture degrades the image as it reaches the macula. Recently, Melki et al.20 studied a standardized method of pinhole testing and found it relatively reliable in estimating the visual outcome after uncomplicated cataract surgery without coexisting disease. Another version of the pinhole test described by Hofeldt and Weiss21 uses a specially illuminated near card (Mini-Illuminated Near Card, Gulden Ophthalmics, Elkins Park, PA). They found that it was useful in predicting postoperative acuity in cataractous eyes with comorbid disease.

Various tests of visual discrimination such as the ability to perceive light coming from various quadrants of the visual field (light projection), to perceive the orientation of the streak from a Maddox rod, and to discriminate between two light sources versus one source of light do not depend on macular function. Even color perception is not a valid measure of macular function, since cone receptors are present in the peripheral retina. The electroretinogram and visual evoked potential are not specific for macular function. These tests do not correlate well with visual acuity in the presence of amblyopia or macular degeneration.

The entoptic phenomenon test is traditionally used in mature cataracts to test for gross retinal function. This phenomenon is created by sweeping a small light source such as a hand-held light from side to side against the eye, usually shining the light through the lower or upper eyelid pointing toward the macular area. The strips of photoreceptors beneath the retinal blood vessels do not have time to adapt when the shadows of the blood vessels move rapidly from side to side, and the shadows become visible as a branching pattern embracing the macula. Perception of the vascular shadows described as seeing veins or vines is a time-honored test for visual function in mature cataracts, but it is not specific for macular function and therefore does not correlate well with postoperative visual acuity in the presence of localized macular disease.

Entoptic phenomena are poorly quantifiable and it is difficult to assign a numeric level of expected visual acuity based on the response of a patient. Using the bluefield entoptoscope, Sinclair and coworkers22 tested 136 eyes prior to uncomplicated cataract surgery. They obtained up to 94% correct prediction of good foveal function and at least 75% correct prediction of poor foveal function. However, Murphy,23 showed less success with bluefield entoptoscopy, especially in dense cataracts. False-positive predictions of potential acuity have also been reported in the presence of macular disorders.

In the presence of dense mature cataracts, if there is serious doubt as to the status of the retina or optic nerve, and thus the outcome of cataract surgery, it may be necessary to perform additional tests such as ultrasonography and computed tomography (CT) scanning.

The following two devices were designed as macular function test devices independent of media opacities in the cornea, aqueous, lens, or vitreous: the potential acuity meter and the clinical interferometer. In actual practice, however, both are effective only in mild to moderate cataracts where there is no macular dysfunction or disease state. However, they have proven to be very useful within these limits, esp. in predicting surgical outcomes in questionable cases, as discussed below.

The Guyton Minkowski PAM (Marco Ophthalmic, Jacksonville, FL)24 projects a standard Snellen chart through a 0.1-mm diameter aperture. This projected chart is directed through small windows in the cataract onto the macula and the patient reads the chart from 20/400 to 20/20. It uses a low-cost incandescent lamp and has a field of vision of 6 degrees.

In the clinical interferometer, beams of coherent light from two point sources are directed to the clearest area of the lens into the retina. Interference fringes in the macula are formed wherever the two beams overlap and by varying the width of the interference fringe pattern, visual acuity can be determined with the Snellen equivalent from 20/660 to 20/20, independent of the optics of the eye. Clinical interferometers use either red helium neon laser light or white light from an incandescent source such as a Xenon Halogen lamp, with a field size ranging from 1.5 degrees to 8 degrees. An example of this is the Heine Lambda 100 hand-held Retinometer (Lombart Co., Norfolk, VA).

In actual use, both the PAM and clinical interferometers underestimate as well as overestimate the potential vision in certain conditions.25 The PAM tends to underestimate the potential acuity in advanced, dense cataracts without any clear zones or openings through which to project the Snellen chart. This is not necessarily a disadvantage in such cases, because the actual postoperative acuity may be much better than predicted, to the pleasant surprise of both patient and surgeon.

On the other hand, clinical interferometers tend to overestimate potential vision in patients with macular disease, such as macular degeneration and amblyopia. In this device the retina has to distinguish the two overlapping coherent light beam fringes as two distinct lines. There may happen to be a few good cones that are situated at just the right position to distinguish these two lines as separate and give a good potential acuity reading. However, there may not be enough cones to recognize a Snellen letter of the equivalent level of acuity. This may result in an overestimation of the potential vision resulting in an unexpectedly poor postoperative vision.

Both the PAM and clinical interferometers are therefore useful to determine the potential acuity and possible outcome of surgery in patients with mild to moderate cataracts. However, they perform poorly in dense opacities, which they cannot penetrate, so that the patient cannot perceive the test objects. Caution should be used when interpreting results from patients with macular disease and amblyopia.2628Tests for Refractive Distortions in the Lens

RESOLUTION TEST TARGET PROJECTION OPHTHALMOSCOPE.

Localized refractive distortions may occur during the development of a cataract, which may distort vision to such an extent that the patient is incapacitated. This may be of major importance to patients with special visual needs, such as surgeons, accountants, bookkeepers, and architects. A device to document these distortions by projecting a series of parallel lines into the retina, which decrease in size to correspond to a Snellen equivalent numerical unit of measure, was developed by the U.S. Air Force29 and modified by Lobo and Weale.30 The Oqual (Zeiss Meditec, Dublin, CA) is mounted on an ophthalmoscope and the examiner views the projected lines in the fundus, grades the degradation of the projected chart image, and documents the degradation of the image using the Snellen equivalent unit.

Recently, wavefront technology,17 using the same idea but more sophisticated methods, promises to be a useful tool in documenting and quantifying the existence of these refractive abnormalities. If the ocular media do not appear opaque enough to explain visual loss (in the presence of an otherwise normal cornea, retina and optic nerve), such refractive lens changes may be responsible and may indicate the need for lens extraction (see under New Methods).

FUNCTIONAL IMPAIRMENT/QUALITY-OF-LIFE TESTS

During careful history taking, the patient usually volunteers typical complaints associated with cataracts, such as painless, progressive loss of vision, difficulty seeing in bright sunlight or at dawn and dusk, increased glare from incoming headlights when driving at night, and difficulty reading road signs. As a result of the vast improvement of cataract and intraocular lens surgical techniques, with the resultant decrease in the complication rate of cataract surgery, criteria for cataract surgery have changed in recent years. These changes allow for earlier surgery if the cataract interferes with the patient's occupation and other activities, combined with the determination (using the potential vision tests described above) that the patient would indeed benefit from cataract surgery. Hence, any visual difficulty with daily activities, as well as the patient's occupational, leisure and social activities, should be inquired about and noted down. A brief statement should be entered into a patient's chart to summarize these discussions, such as: The patient's visual function has decreased to a level that interferes with the patient's ability to carry out normal daily activities. In addition, given the mental status and physical abilities of the patient, there is reason to expect some surgical benefit in function and personal comfort and/or activity. This can be added to the consent form also, with the statement that possible complications with eye surgery were discussed with the patient. These discussions with the patient and their proper documentation in the chart play a crucial role in the decision making in cataract surgery as well as in litigation when there is a problem as to the outcome of cataract surgery.

Recent research has also revealed the interesting observation that in older patients, cataracts may play an important role in the causation of car accidents,31 falling accidents resulting in fractures,32 and mortality and functional decline.33 Hence, earlier visual rehabilitation through cataract/IOL surgery is becoming not only an option but a necessity.

Recently, more detailed and standardized methods of documenting these visual and functional disabilities have been developed, especially for clinical research purposes.

National Eye Institute Visual Function Questionnaire: 25 Items (VFQ-25)

The National Eye Institute Visual Function Questionnaire: 25 Items (VFQ-25) was developed under the sponsorship of the National Eye Institute with the goal of creating a survey that would measure the dimensions of self-reported, vision-targeted health status that are most important for persons with chronic eye problems.34 The survey measures the influence of visual disability and visual symptoms on patients' daily visual functions as well as other health domains such as emotional well-being and social functioning. It consists of a base set of 25 vision-targeted questions representing 11 vision-related constructs, plus 1 general health rating question. It takes approximately 10 minutes for an interviewer to administer. There is also a self-administered format. The VFQ-25 forms (revised 2000), as well as additional information, can be obtained from the website of the National Eye Institute (www.NIH.GOV).

Visual Function Questionnaire14 Items (VF-14)

The Visual Function Questionnaire14 Items (VF-14) was developed by a team from the Johns Hopkins University Hospital and Georgetown University Hospital as a measure of functional impairment caused by cataract and provides information not conveyed by visual acuity or a general measure of health status. It has also been shown to be sensitive and reproducible.35,36Others test such as the Short Form-36 Items (SF-36),37, 38 Activities of Daily Vision (ADV),39 and Sickness Impact Profile (SIP)40 are other measures of functional impairment that have been used in clinical research on cataract patients.

OPHTHALMOLOGIC CLINICAL EXAMINATION

Hand-Held Light Examination

Field eye examinations, such as done in epidemiologic studies and surveys, can be facilitated by the use of a hand-held light in conjunction with a head-mounted or spectacle-mounted magnifying loupe, ideally inside a darkened room (to promote mydriasis). Because one is looking mainly for visually significant cataract, information obtained with this method, together with a Snellen visual acuity measurement, is the usual end point for these studies. More sophisticated equipment such as an ophthalmoscope and a hand-held slit lamp biomicroscope will be needed if a more precise classification and grading of the cataract is needed.

Ophthalmoscopy

The use of the direct ophthalmoscope's built-in +10 lens both with direct illumination and retroillumination using the light reflected from the fundus allows the detection of opacities in the lens, especially in field situations. However, the two-dimensional monocular view, the limited magnification and the short working distance makes ophthalmoscopy inadequate for thorough cataract evaluation. The indirect ophthalmoscope may also be useful in making a gross assessment of the clarity of the media as one looks at the fundus. Experienced clinicians performing indirect ophthalmoscopy can often gauge the amount of vision loss from the haziness in the ocular media that they observe. These are gross assessments, however, and are inferior to information obtained from the slit-lamp biomicroscope.

Other Accessory Devices

Ultrasonography (A and B scan) is used routinely to obtain measurements (axial length of the eye, anterior chamber depth, lens thickness) needed for intraocular lens power calculation. In completely opaque, mature cataracts, it is also useful in determining the status of the vitreous and retina. Specular microscopy of the lens epithelium (originally developed for the cornea) is also being used to study age-related changes41 as well as changes in the lens epithelium in special cataracts such as the myotonic dystrophy cataract.42 Confocal microscopy (originally used in vivo on the cornea) is also being tried on the lens in vivo, and promises to be useful in the future.

Slit-Lamp Examination

The optimum way of examining the lens clinically is using the slit-lamp biomicroscope through a widely dilated pupil. This instrument provides a three-dimensional view of the lens. One can focus on specific areas of the lens from different angles, and at the same time vary the location, direction, and intensity of the illuminating beam independently. The following techniques can be used: (1) direct focal illumination using either a wide or narrow beam; (2) retroillumination; and (3) others including specular reflection, indirect illumination, diffuse illumination, and use of the light reflected from the iris and posterior capsule.

In direct focal illumination, the slit beam is positioned directly on the area being studied. One can use various configurations of the slit beam, but the most useful way is a narrow beam to produce the cross section of the lens. The light is slightly attenuated by passage through the cornea and undergoes refraction, reflection from the surfaces (zones of discontinuity), scattering, absorption, polarization, and fluorescence.

Vogt43 first used slit-lamp biomicroscopy using the narrow beam (0.1- to 0.5-mm thick) to study the lens and described the various zones of discontinuity denoting the layers of the lens fiber cells laid down during a patient's lifetime. These zones represent lenticular growth periods and aid in determining time of origin of opacities. Because of the narrow depth of focus of the biomicroscope, the examination begins at the anterior capsule and gradually focuses deeper to see the various layers. The zones of discontinuity are the shells of the nucleus and cortex that are concentric to each other (Figs. 2, 5, 6, and 7).

Fig. 2. Brunescent (brown) nuclear cataract using (A) narrow beam slit illumination and (B) retroillumination. The cataract is best seen by direct slit illumination. In retroillumination, as seen in this image, the outline of the nuclear cataract may be seen due to its increased refractive index, although the cataract does not cast any shadows. Because of its central location, this cataract may cause distortion of images early in their development.

Fig. 5. Scheimpflug slit-lamp photographic images of: (A) normal; (B) cortical; (C) nuclear; and (D). Posterior subcapsular cataracts. The Scheimpflug method allows for slit-lamp imaging wherein the entire lens is in focus. The gray scale on the left of each image was built-in to aid standardization of the image during densitometry (for objective quantification of the opacities).

Fig. 6. Automated densitometric analysis of a digital Scheimpflug slit image of a normal 50-year-old lens. Because of the characteristics of the lens layers, the location of the cortex and nucleus can be automatically detected by special software, and with automated densitometry, mean optical density values can be easily and quickly obtained for analysis. Thus, automated detection, classification, and grading may be possible. Note the concentric layers of lens fibers in the cortex and the nucleus.

Fig. 7. The Lens Opacity Classification System II (LOCS II) photographic grading standards. N = Nuclear photographs. Stage 0 = normal; IIII = various stages of nuclear cataract. For nuclear opalescence, the average opalescence across the entire nuclear region is used. An opalescence that is less than or equal to Photographic Standard 0 = grade 0; if the opalescence is less than or equal to Standard I, the grade is 1, and so on. For Color Grading of the nucleus, only the N2 standard is used. ( ). P = Posterior subcapsular photographs. 0 = normal; IIII = various stages of posterior subcapsular cataracts (Chylack LT, Leske MC, McCarthy D, et al: Lens opacities classification system II [LOCS II]. Arch Ophthalmol 107:991, 1989. Copyright 1989, American Medical Association with permission.)

The lens nucleus can be divided into embryonic, fetal, infantile, and adult. The embryonic nucleus is a clear central zone found between two cotyledons that make up the fetal nucleus. These cotyledons are similar to mirror halves of a peanut. The infantile and adult nuclear zones lie over this. The sutures classically described as y-shaped are points of convergence of the anterior and posterior tips of the lens fibers and may vary in shape.4445 Recent research suggests that abnormalities in suture shape, which reflect abnormalities in lens fiber development and/or maturation, may signify a predisposition to the development of cataracts later in life.46 The nucleus increases in thickness and density with increasing age. The lens cortex lies between the nucleus and the capsule and varies in thickness. It is usually clear although some isolated dots may be present normally. The lens capsule is thicker in the front than in the back and is the basement membrane of the lens epithelium isolating the lens from the rest of the eye.46Direct focal illumination using the narrow beam is useful not only in studying the anatomy of the lens but also in examining minute opacities to localize their position and estimate their size. Nuclear cataracts tend to scatter light so that narrowing the beam prevents the washout effect and allows examination of details as well as enhances patient comfort. The Scheimpflug camera (see below) was developed to increase the depth of focus of images obtained with the slit lamp (Figs. 5 and 6) and is ideal for documenting slit images of the lens, and especially nuclear cataracts.4748 It uses a fixed narrow beam and obtains reproducible images in which the whole-lens thickness is in focus. These images can be examined by densitometry for statistical comparison with other images of the same patient taken over time to document and track changes.

The broad beam is useful for examining cortical cataracts especially spokes and water clefts (Fig. 2), which tend to be large and irregular. It is also useful in posterior subcapsular cataracts, particularly in the early stages, which can be detected by irregular grainy reflection from the otherwise mirror-like sheen of the posterior capsule. Abnormalities in size and position of the lens are also assessed by using either broad or narrow beams.

Retroillumination uses the light reflected from the fundus to highlight opacities. This is very useful in examining cortical and posterior subcapsular cataracts (Figs. 1, 3, 7, and 8). However, some cortical water clefts and early posterior subcapsular opacities may not be easily seen with retroillumination if they are not dense enough to cast shadows or only refract the retroilluminate light; these can be best seen with the broad beam. Using retroillumination on nuclear cataracts does not give much information because these usually do not cast shadows. However, as seen in Figure 2B, a change in the refractive index can be seen toward the center. Usually, the outline of the nuclear cataract can be seen as a result of a magnifying lens artifact. This is also easily observed during direct and indirect ophthalmoscopy. Several retroillumination cameras (modified slit lamps with the slit beam fixed for retroillumination and depolarizers built in to remove corneal reflex from the image) have been developed and are being used for documenting cortical and posterior subcapsular cataracts.49, 50

Fig. 3. Posterior subcapsular cataract (PSC) using (A) direct illumination and (B) retroillumination. PSCs usually start centrally and extend toward the periphery. For this reason, they interfere with visual function, causing glare disability early.

Fig. 8. Follow-up retroillumination photographs of an eye with a cortical cataract, obtained at various intervals. A. First visit (1-21-87); B. 1 year later (1-27-88); C. 22 months later (11-14-88); D. 28 months later (12-4-89); E. 35 months later; F. 41 months later (6-18-90). With such photographs one may be able to plot the progression rate of a cortical cataract, and aid in performing longitudinal studies. Note the central opacity, which is out of focus and represents a small posterior subcapsular cataract.

The surfaces of the anterior and posterior capsule may be studied using specular reflection. A bright reflex or shagreen is usually seen as the beam is moved from side to side across the surface of the lens. When examining the lens epithelium, for example, this can occur when the observer focuses on the lens surface and the angle of incidence of the beam is equal to the angle of reflection. The clinical specular microscope developed for the corneal endothelium has also been especially adapted for study of the lens epithelium.41,42In summary, slit-lamp biomicroscopy is the most useful method for clinically detecting and localizing lens opacities, determining their extent and density, and monitoring changes over time.

SLIT-LAMP PHOTOGRAPHY OF THE LENS AND GRADING OF CATARACTS

Slit-lamp photography has been used to document anterior eye segment disorders, including abnormalities and opacities in the lens, since camera attachments to slit lamps became available. Variables to consider in its use in the lens include the limited depth of field, the variabilities in light intensities with the slit beam, limits of magnification with corresponding limits on the area that can be photographed, limits in the angle of the slit beam used, and limits imposed by pupil size. The advent of digital cameras has made lens documentation even more useful. The examiner can check the image quality while the patient is still on the slit lamp. Patients and their families are often grateful to see the lens pathology during the consultation. This facilitates their active participation and cooperation in any discussion and decision making, especially if intervention is required. These images can also be sent electronically to distant tertiary centers for quick consultations or stored in disks immediately for easy transport as well as inclusion in a patient's chart.

Recently, cataract classification systems have been developed that use carefully selected slit lamp photographs of cataracts as standards for comparison with the patient's cataracts. These include the following: the Lens Opacities Classification System (LOCS) version I,51 version II (Fig. 7),52 and version III,53 the Wisconsin Cataract Grading system,54 the Wilmer Cataract Grading System system,55 the Oxford Cataract Grading System system,56 and the Age Related Eye Diseases Study (AREDS) Cataract Grading System.57,58 These systems are similar in that they provide lens photographs or films showing various severities or grades of cortical, nuclear and posterior subcapsular cataracts to be used as standards, which a clinician can then compare to the patient's cataract as seen directly on the slit lamp. For nuclear cataracts, slit photographs of the lens are used, and for cortical and posterior subcapsular cataracts, retroillumination photographs are used. Instructions are provided for the clinical use of the systems, specifically what borders or cutoff points are to be used for using each standard image. Figure 7 shows the LOCS II standard photographic plate. Another recently described system that was designed to be simple and easy to use on the slit lamp, especially for field cataract assessments, is the World Health Organization cataract grading system.59Another way of using these classification schemes is to obtain slit-lamp photographs of a patient's cataract following a specific photographic procedure described by the authors of each system. These photographs can later be read by a reading center or by the clinician, comparing the patient's photograph with the standards. With the advent of digital cameras and the possibility of automating most of the photographic processing of the images, this method may become easier with time. At present, it is only used in clinical research studies and is expensive, cumbersome, and impractical for regular clinical use.

Modified Slit-Lamp Photography

Several instruments have been developed to convert the cataract image into numbers in a more sophisticated way. These use either 35-mm film or digital cameras to capture the images, which are then digitized onto a computer. In nuclear cataracts, densitometric analysis of the cataract image is then performed to convert the values into optical density units. In cortical and posterior subcapsular cataracts, the area occupied by the cataract can be measured in square mm. These values can then be analyzed statistically.

SCHEIMPFLUG CAMERAS.

Slit lamps modified along the Scheimpflug principle (Fig. 9)47,48 can obtain lens images with enough depth of focus so that the entire anterior chamber from the cornea to the posterior capsule of the lens are in sharp detail (see Figs. 5 and 6). Usually, the slit beam is set at 45 degrees away from the image plane of the camera, which is focused on the lens parallelepiped (Fig. 9). The available charged-coupled device (CCD) cameras, which are supplied with computer hardware and software, use a slit beam with a fixed thickness and level of illumination and obtain images that are reproducible, easily stored in portable disks, and easily analyzed using built-in densitometers. The operator can manipulate the software to designate which area to analyze and the average density is expressed either in optical density units or gray scale/intensity values. Among those available currently are the Nidek EAS-1000 camera (Scheimpflug Unit, Nidek Tech, Inc., Pasadena, CA) and the Oxford Scheimpflug camera (Marcher Enterprises, Hereford, U.K.). Figures 5 and 6 show Scheimpflug images of a normal lens and various types of cataracts obtained using a Scheimpflug camera, and two ways to analyze these images to obtain the mean density of various areas within the lens.48,50 Longitudinal studies, such as for following the progression of nuclear cataracts, can thus be conducted in an objective and masked fashion.48

Fig. 9. Scheimpflug principle: When an object plane (slit beam), objective plane (camera lens) and image plane (film plane) intersect, the result is a photograph with a deep depth of focus.47 On most Scheimpflug slit cameras, the slit beam and charged-coupled device (CCD) camera are at 45 degrees angles to each other, and the anterior eye segment (cornea to lens posterior capsule) is in focus in the resultant image.

RETROILLUMINATION CAMERAS.

Retroillumination cameras49,50 obtain images of cortical and posterior subcapsular cataracts as shown in Figures 1B, 7, and 8. These are useful for both cross-sectional and longitudinal studies. Various manual or automated methods have been developed or are being developed for the analysis of these images to determine the size of opacities. Usually, an artificial mask with a chosen diameter is used to standardize the area of interest in the image, and either a percent area or area in square millimeters is determined. Because of the variability of the background light (the images are shadows of the cataracts using light that is backlighted from the retina or optic nerve), densitometry is unreliable. Among the methods used include computer planimetry, counting boxes, manual and automated edge detection, and automated area analysis. This method is also being used to study IOL decentration and posterior capsular opacification after cataract surgery. Examples of this type of device are the Nidek EAS 1000 retroillumination unit (Nidek, Pasadena, CA), Oxford retroillumination camera (Marcher Ltd., Hereford, UK), and Topcon CTR (Topcon Medical Systems, Paramus, NJ).

Other Specialized Slit-Lamp Imaging Systems

Various innovators have devised specialized slit-lamp cameras with improved acquisition and image analysis of cataracts. The Laser Slit Lamp (Bausch and Lomb Surgical, San Dimas, CA)60 was developed to measure the density of nuclear cataracts. The Sequential Color Cataract Imaging System,61 provides three lens images for analysis: (1) saggittal sections of the lens, (2) retroillumination images, and (3) images of opacities obtained by direct or side illumination. These devices promise to be useful in clinical studies of the lens and cataracts but may need further development and standardization.

In summary, the use of slit and retroillumination imaging coupled with a computerized analysis system is presently the state of the art in objectively measuring cataracts. However, because of the expensive equipment, the extra time, space, labor, and effort required, and limited practical clinical use, these systems are presently used mainly in clinical research settings. The clinical judgment of the ophthalmologist based on the history and eye examination remains the standard in clinical practice.

NEW METHODS UNDER DEVELOPMENT

New technologies are being applied in the study of cataracts and show great promise for providing new insights into the cataract problem, as well as new devices that a clinician can use with cataract patients in the clinic. In this section, the following devices are discussed: quasielastic or dynamic light scattering (QELS or DLS), magnetic resonance imaging (MRI), spectroscopy, wavefront technology, Raman spectroscopy, autofluorescence, and optical coherence tomography (OCT). These new noninvasive techniques add to the armamentarium available to cataract researchers. Steps being taken to develop these devices for noninvasive clinical use in vivo aim for their possible use on patients for diagnostic purposes in the near future.

Quasielastic or Dynamic Light Scattering

The intense scattering of light by a cataract arises from a change in the interaction and organization of the constituent particles/lens proteins mediated by lenticular stress. These changes in interaction and organization are reflected in altered motional dynamics (translational and rotational diffusion) of the lens proteins in the cytoplasm. The investigation of lens protein dynamics is being successfully accomplished by the use of DLS.62DLS is an established laboratory technique to measure the average size or size distribution of microscopic particles (3 nm to 3 m) suspended in a fluid medium in which they undergo random Brownian (or thermal) motion. Intensity of light scattered by the particles from a laser beam passing through such a dispersion will fluctuate in proportion to the Brownian motion of the particles. Because the size of the particles influences their Brownian motion, analysis of the fluctuations in scattered light intensity yields a distribution of the diffusion coefficient(s) of the suspended particles from which average particle size or particle size distribution can be extracted. In these experiments, visible light from a laser is focused into a small scattering volume inside a sample. The scattered light is collected using a photodetector (photomultiplier tube or an avalanche photodiode) and is processed via a correlator that yields a time correlation function (TCF). For dilute dispersions of spherical particles, the slope of TCF provides a quick and accurate determination of the particle's translational diffusion coefficient. This can then be correlated to the size of particles in the solution via a Stokes-Einstein equation, provided the viscosity of the suspending fluid, its temperature, and its refractive index are known.62-66 The distribution of particle size obtained from the tissues examined (such as the lens) can then be plotted (Figs. 10 and 11).

Fig. 10. Data obtained from a cold-induced cataract study using calf eyes. Data on the left show the size distribution of lens proteins as the cold cataract appears (as the temperature of the calf lens is lowered) showing the shift from small to large molecular weight proteins (data obtained from the dynamic light scattering [DLS] device) versus Scheimpflug slit-lamp images of the same calf lens as the temperature is correspondingly lowered and the cold cataract appears. The DLS device picks up a shift in protein size much earlier than the Scheimpflug camera shows the appearance of the cataract.66

Fig. 11. Comparison between distribution of particles in a normal human lens versus a nuclear cataract obtained clinically (in vivo) on patients using the NASA-NEI clinical dynamic light (DLS) device.64,66Clinically, DLS can be used to study cataracts noninvasively at the molecular level. It is safe and fast to use in early cataract evaluation because of the very low laser power (50100 W) and short data acquisition time (5 seconds). In a cold-induced cataract model experiment in which the cataract was simultaneously monitored with both the DLS device and Scheimpflug camera (Fig. 10), the DLS picked up subtle changes in the lens quicker (23 orders of magnitude earlier) than the Scheimpflug camera.66 The DLS measures the Brownian motion of the crystallins inside the lens. The major proteins that can scatter light in a human eye lens are -, -, and -crystallins. The -crystallins are the largest molecules (molecular weight, 106 daltons) and they induce the greatest amount of light scattering in a DLS measurement. When these protein molecules aggregate, they give rise to lens opacities.

For clinical use, DLS probes can also be integrated with slit-lamp, Scheimpflug, and autofluorescence instruments because of the current modular design. Data obtained from patients in clinical studies have shown good reproducibility.65,66 For clinical purposes, it has been suggested that the log 10 mean particle size be used as a clinical end point for this device.66 However, more studies are needed to further understand the wealth of data obtained with this device. Its application in eye research is just being explored, and much information can be obtained not only on the lens but also on the cornea,67 vitreous, and retina.68,69Magnetic Resonance Imaging and Nuclear Magnetic Resonance Spectroscopy of the Lens

As any other human tissue, the lens contains carbon and hydrogen atoms in which protons spin around their nuclei in random directions. On application of a magnetic field, these microscopic magnets are aligned in a particular (north-south) direction (higher energy state). On turning off the magnetic field, the microscopic magnets return to their original random state (lower energy state). The frequency of rotation is equal to the energy of a photon (normally a known radio frequency) that would cause the nuclei to flip between these two energy levels. This provides measurements of relaxation rates between different energy states of the nuclei in relation to the applied excitation photon field. Because they are dependent on the hydrogen nuclei densities in the tissue, the relaxation rate information can be translated into images.

MRI provides the ability to probe the chemical and metabolic status of the lens noninvasively. Thus, in response to normal and pathophysiologic conditions, areas such as lens metabolism, ion concentrations, the state (bound versus free) of lens water, and metabolite and macromolecular motional dynamics may be investigated. Valuable biochemical and biophysical information pertinent to the factors that govern lens transparency, and conversely, the medical condition of the cataract can thus be studied.

MRI has been used to image the eye but problems have been encountered including poor resolution; limited access to the surface coil and poor resultant magnetic signal (because of the location of the eye within the bony structure of the orbit); motion artifacts (caused by microsaccadic eye movements, breathing and heartbeat); and the presence of high susceptibility gradients around the eye. Recently, Lizak et al.70 used a special technique, magnetization transfer constant enhancement (MTCE), to enhance the lens image successfully and study diabetic and galactosemic animal models of cataract, and have applied it to clinical use. MTCE takes advantage of the magnetic interactions between water and macromolecule hydrogen atoms.

Preliminary clinical studies suggest that cortical lens changes can be better observed with unenhanced magnetic resonance images, whereas nuclear lens changes are better observed by the addition of the MTCE preparation pulse (Fig. 12). MRI, therefore promises to be an imaging method independent of optical imaging that will allow clinicians to monitor metabolic processes in the lens.70

Fig. 12. Sagittal section images of a nuclear cataract. M0: Magnetic resonance image (MRI) of a patient's eye with a nuclear cataract, taken in vivo and noninvasively. Scheimpflug: Image of the same nuclear cataract (LOCS II nuclear opalescence grade 2) taken using a Zeiss Scheimpflug slit lamp camera (optical/digital). Ms: MRI image of the same eye with magnetic transfer contrast (MTC) enhancement (see text).

13C nuclear magnetic resonance (NMR) spectroscopy of the intact lens, on the other hand, has provided information about the production, turnover, and inhibition of sorbitol by aldose reductase inhibitors. Proton NMR spectroscopy of 13C-labeled metabolites offers the ability to monitor the reactivation and dynamics of the hexose monophosphate shunt (HMPS), a pathway important for the maintenance of the lens redox state, in real time and noninvasively.7131P NMR spectroscopy allows the monitoring of the phosphorus-containing metabolites, thereby permitting the real-time assessment of lens tissue metabolic response to pathophysiologic conditions. Important metabolites, such as adenosine triphosphate, phosphomonoesters, and phosphodiesters may be monitored. Furthermore, intralenticular pH may be measured. However, no clear correlation between phosphorus metabolite levels and lens clarity has been established to date, despite numerous NMR and classic biochemical studies. This lack of correlation suggests the importance of biophysical investigations aimed at the interaction behavior and organization of the constituent lens proteins in the cytoplasm, the macromolecular entities responsible for light scattering associated with cataract.72NMR spectroscopy may be viewed as an important adjunct to the better established laser light scattering studies of the lens, and has remained mainly a laboratory, rather than a clinical, method of studying the human lens.72Wavefront Technology

Image degradation in the macula because of cataract may not only be caused by light scattering but also by optical aberrations. As discussed above (see Visual Acuity/Function Tests), several devices such as the Oqual and resolution test target test have been devised as simple ways to test for the effect of optical degradation in the retina.

A new technology using wavefront analysis to study optical aberrations of the eye and in particular the cornea to enhance the results of refractive surgery in patients has also been used on the lens. Kuroda et al.,17 using the Hartmann-Shack (H-S) Aberrometer (Topcon Corp., Tokyo, Japan), found that ocular total higher order optical aberration in eyes with a cortical or nuclear cataracts was significantly higher than in normal subjects. Corneal total high-order optical aberration in eyes with mild cortical or nuclear cataracts did not differ from normal subjects. This suggests that high-order optical aberration increases in eyes with cataract because of the local refractive change in the lens. Another finding was that the polarity of spherical aberration was different between nuclear and cortical cataracts. In nuclear cataract, the polarity is always negative, suggesting a delay of the light wavefront occurs when the ray travels inside the hard nucleus with increased refractive index. In contrast, in cortical cataract, the polarity was always positive.

These findings suggest that in mild cortical and nuclear cataracts, not only light scattering but also optical aberrations in the lens contribute to loss of visual function as measured by loss of contrast sensitivity.17 Thus, this new technique may be useful in studying the total effect of early cataracts on visual function, and explain some patient complaints such as monocular diplopia, in the presence of mild lens changes.

Raman Spectroscopy

Raman spectroscopy is routinely used as an analytical tool in chemistry laboratories. It is a light-scattering technique based on the Raman effect, which was discovered in 1928. The light (or photons) impinging on a molecule interacts in various ways but the final outcome always results in the scattering of light. For example, we do not see light directly. We always see light and objects as a result of scattered light. Scattering is absorbance of incident light used in exciting the atom and reradiation of this light. The Raman scattering is the result of inelastic collisions in which the scattered photons exchange energy with the vibrational energy modes of an atom. This frequency shift (or the difference in frequency of an incident photon and the scattered photon) points to specific structural information about a constituent molecule analogous to a certain specific fingerprint that can identify any species present in the system being investigated. However, the Raman signal is very weak. Of 1061010 incident photons only one scattered photon exhibits a Raman shift. Because of this, the Raman method has remained limited to chemistry research laboratories since its discovery.

Raman spectroscopy has furthered our knowledge of normal aging and pathologic processes in the lens73 that would not have been possible with other currently available methods. The structural information it provided includes: SH, SS, H2O, Trp, Try, Phe, and protein secondary structure. Studies can be carried out in the intact living lens, thus avoiding any protein disruption or possible autooxidation of sulfhydryl inherent in studying isolated protein fractions of lens. Using the optical dissection technique, the Raman scattered light can be analyzed from any portion of the lens along the visual axis (or along any axis). This technique monitors aging changes within the lens so that older nuclear proteins can be easily compared with those newly synthesized in the cortex. By coupling with an optical microscope, laser Raman instrumentation has been transformed into a unique imaging device with excellent spatial resolution.

Raman spectroscopy has also been used to demonstrate regional swelling of the lens in diabetes. In mildly diabetic rats, the overall increase in lens hydration is hardly detectable. However, regional swelling was demonstrated by Mizuno et al.74 with this noninvasive technique. This method permitted determination of water content from the periphery of the lens to the center. The advantage of this type of noninvasive technique, similar to that of NMR spectroscopy and QELS, is that it permits analysis of discrete areas of the lens. Thus, these methods may be helpful in determining the changes that occur in certain regions of the lens during cataract formation. The Raman spectra of animal and human lenses has been discussed by Ozaki in a review article.75Clinical in vivo use of this technology is limited by the need to use high laser power, and comprehensive spectral data libraries must first be generated and established. It then can be used as searchable fingerprints (indices) for ocular and other diseases.

Autofluoresence Spectroscopy

Ocular tissues exhibit natural or auto fluorescence (AF) and it has been found to increase with age in healthy individuals.76 Accumulation of fluorescent proteins in ocular tissue can result from long-term exposure to the UV or UVA radiation in sunlight. This accumulation of fluorophores may also be responsible for lens opacification and can be considered a risk factor for cataract formation. These fluorophores can be found during cataract formation. In initial stages these can be characterized by exhibiting fluorescence in the near ultraviolet and violet regions of the spectrum (340 and 411 nm). However, in advanced stages of cataract development an increase in the intensity of the long-wave fluorescence of the lipids in the blue-green region (430/480 nm) occurs.77 AF from transparent (noncataractous) lenses exhibits a strong correlation as a function of age (Fig. 13). In this figure, the increased level of fluorescence from the lens can be attributed to oxidative stress or absorbance of UV light as a function of age. Because the cornea does not absorb UV, its AF level remains constant. However, both diabetic lens and cornea show significantly increased AF levels.

Fig. 13. Natural autofluorescence of the eye with aging.

Studies of the AF properties of the ocular media have shown that ocular AF can be related to metabolic disorders.78,79 Thus prepathologic states can easily be studied by measuring AF intensity from the corneal tissue because it is readily accessible (no dilation needed) and its intensity is not age-dependent. Corneal AF is mainly the result of the pyridine nucleotides and flavoproteins found in the corneal epithelium and the endothelium. The accumulation of these fluorophores can be related to the severity or duration of some pathologies and therefore the corneal AF can be exploited as a diagnostic index of this class of disorders. In particular, an increase in the corneal AF has been observed in the presence of early stage diabetic retinopathy (DR)80 by using a novel instrument.81Optical Coherence Tomography

OCT is a near-infrared optical ranging imaging technique. The images obtained by OCT are of much higher resolution (approximately 115 m) compared to images obtained by low-frequency ultrasound, pulse-echo imaging (approximately 100 m). The two-dimensional image of optically reflecting and backscattering from tissue microstructure in OCT is constructed using low-coherence interferometry. Photons that have scattered multiple times (multiple scattering) are rejected by coherent detection because it takes advantage of short temporal coherence of broadband light source, e.g., light-emitting diodes (LEDs). The interferometric system selects photons that have traveled a specific distance in the tissue. The beam scans turn the one-dimensional depth profile into a two-dimensional image. The images are similar to that of histologic sectioning. At present this technique is being used to obtain retinal images. High-resolution OCT images provide detection of subsurface retinal changes that are not seen by ophthalmologists in conventional settings. This is important in monitoring injury to the optic nerve from glaucoma. Most biologic tissues highly scatter in the visible and near-infrared range.

In ophthalmology, OCT represents a novel, noninvasive, noncontact transpupillary tool, which can image the fine anatomic structures within the eye, structures too fine to be adequately assessed by conventional techniques. The appearance of a variety of anterior/posterior segment pathologies can be diagnosed using OCT including cataract, glaucoma, diabetic retinopathy, macular holes, epiretinal membranes, cystoid macular edema, central serous choroidopathy, and optic disk pits.8285 Although OCT has been shown to image cataracts, it has not yet been used extensively in this area.

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HYPERLINK "http://www.ncbi.nlm.nih.gov/books/n/cm/A3603/" \o "Next page in this title" Next >Chapter 117The Funduscopic Examination

Henry Schneiderman.

Definitions

Funduscopic examination is a routine part of every doctor's examination of the eye, not just the ophthalmologist's. It consists exclusively of inspection. One looks through the ophthalmoscope (Figure 117.1), which is simply a light with various optical modifications, including lenses. The ophthalmoscope illuminates the retina through the normal iris defect that is the pupil. Light rays forming the image of the retina re-emerge through the pupil. The viewing aperture (window) of the ophthalmoscope contains a lens that modifies light rays to assist the user. In the procedure, one looks at structures lying in the innermost aspect of the globe, collectively known as the eyegrounds: retina, retinal blood vessels, optic nerve head (disk), and to a limited degree, subjacent choroid. The pupil is frequently dilated pharmacologically to render retinal inspection easier, and for examination of the macula. One paralyzes the pupilloconstrictor muscle of the iris with nonabsorbable, short-acting topical parasympatholytic drugs, resulting in a larger pupillary aperture. In comparison to the ophthalmologist, the internist, neurologist, or pediatrician concentrates particularly on funduscopic manifestations of systemic disease and less on local ocular disease. Synonyms for funduscopic examination include funduscopy, ophthalmoscopy, and direct ophthalmoscopy. Only ophthalmologists perform retinoscopy and indirect ophthalmoscopy, which require other equipment and provide different information.

Figure 117.1The instrument. (A) A portable ophthalmoscope in front (patient's-eye) view. a. Rheostat runs along circumference of tube and controls intensity of beam output. In wall-mounted instruments, this is located instead on the fixed panel, b. Handle containing (more...)The term temporal is used in describing ophthalmoscopic landmarks and findings, rather than "lateral"; and nasal replaces "medial." The optic nerve head or disk is seen when one looks through the pupil from an angle about 15 degrees temporal to the optical axis (the patient's line of sight, "straight ahead"). The disk is a yellow-pink color that stands out from the redder, browner, or more orange retina proper (see Figure 117.4D). The disk is sharply demarcated temporally and to a lesser degree nasally from the background retina, which is all the retina that is not disk, vessels, or macula. Frequently, a narrow crescent of stippled pigment adjoins the sides of the disk, especially the temporal side (house staff have called the author to see "lesions" that turned out to be this normal feature). The disk is slightly taller than wide. The central part of the disk is paler, and is called the optic cup or physiologic excavation; normally this occupies less than one-third the diameter of the disk. In glaucoma and in high myopia the cup is enlarged. The transverse diameter of the disk is a standard yardstick in fundal description, so that, for example, a lesion may be characterized as "one-half disk diameter out at two o"clock, and extending two disk diameters superiorly therefrom." Although some examiners realize that the disk is 1.5 mm wide, nobody describes a lesion as 3 mm across. Near mid-disk, the central retinal artery and vein emerge from the optic nerve, with which they have run forward into the orbit. Each soon bifurcates into superior and inferior branches, which run "flat," that is, parallel with the retinal surface. Beyond one disk diameter out, they are called arterioles and venules. With all retinal vessels, the artery/arteriole appears slightly smaller, and distinctly lighter, more orange-red and less purple than the vein/venule. The color difference reflects the contained blood column that is visualized: the vascular walls are transparent, and deoxygenated venous blood is darker than arterial blood. Before it crosses the disk edge, each large vessel divides into a nasal and a temporal branch. Thus the principal arteries, veins, and quadrants of any retina are the superior temporal, inferior temporal, inferior nasal, and superior nasal. The avascular, dusky area two disk diameters due temporal to the disk is the macula. This is the area of greatest visual acuity. Apart from this zone, the background retinal color will parallel the patient's skin and hair pigmentation, from pale in light-skinned blondes to an umber shade in the darkest black people.

Figure 117.4The value of pupillodilation. (A) External examination shows miotic pupil at baseline. (B) Scant fundus is revealed through this pupil. (Peripheral clouding is an artifact of photography through undilated pupil; actual funduscopy in this case showed retina (more...)Normally, the largest veins pulsate slightly and the arteries do not, the reverse of the situation elsewhere in the body. No hemorrhage is seen in normal fundi. Any yellow, yellow-white, gray, or black interruptions of the background retinal color pattern suggest pathologic exudate, edema, or scar. No wrinkling of the retina should be seen. Chalky whiteness or erythema of the disk is abnormal, as are indistinct disk margins. Any sharp change in elevation that renders one area out of focus with the ophthalmoscope, while the remainder of the retina remains in focus, is abnormal. Tortuous blood vessels usually bespeak pathology.

Technique

The Instrument

Spend time becoming accustomed to looking through the ophthalmoscope in a nonpressured setting. Hold the instrument with the hand ipsilateral to the examining eye; both are ipsilateral to the eye being examined: examine every left fundus with your left eye, holding the ophthalmoscope in your left hand (Figure 117.2); and every right fundus with your right eye and hand. Students with strong dominance of one eye may at first experience difficulty and anguish employing the other eye. They always gain success and comfort in time. The forefinger turns the horizontal rheostat and the vertical lens wheel. A portion of this lens wheel, containing a single lens, overlies the window at any given setting. Lenses have red numbers for negative diopter values (progressively more distant focusing with higher numbers); black numbers are positive (i.e., higher black numbers mean shorter focal length). Of the several light beams available, only the two plain white circles are important to the generalist. The larger illuminates a wider field, but the smaller decreases corneal glare. Hold the instrument against your bony orbit, with the bumper ridge against your forehead. Practice will show how to focus it. The ophthalmoscope does not magnify images except slightly at high positive diopters. Rather, the fundus appears magnified at funduscopy because of the magnification produced by the patient's lens; aphakic fundi look tiny and far away through the ophthalmoscope. Practice turning your head and craning your neck every which way, while maintaining a constant relationship between your eye, your hand, and the instrument. A viewing aperture moved 1 mm out of your optical axis can mean loss of half the available field, so make the spatial relations as constant as though yoked.

Figure 117.2Holding the instrument. (A) Examiner correctly holds the ophthalmoscope in the left hand and looks through it at subject's left eye, using her own left eye. All three organs are ipsilateral! (B) Bungler employs left hand and crosses over. He uses his (more...)The Procedure

Lower the room lights. Remove your and the patient's eyeglasses, but not contact lenses. Have the patient hold her glasses or put them someplace safe. Give the patient a tissue in case of tearing. Show the patient a spot directly ahead of her, on which to fix her gaze. An object or picture 1 m ahead is perfect. She will be able to fixate only with the eye that is not being examined (i.e., that is not being blocked and spotlighted by the examiner). Do not interview during ophthalmoscopy; people involuntarily turn their eyes toward a speaker, and that is the end of visualization. Hold the ophthalmoscope to your eye so that you can see well through it. Keep your other eye open, but ignore its input for now.

Begin with your light at two-thirds strength. Stand 15 degrees temporal to the patient's optical axis, your eye 30 cm from hers. Set your lens wheel at + 10 diopters. Trans-illuminate the pupil and observe reflected red light, the red reflex. Place your contralateral palm on her forehead, with your abducted thumb on her supraorbital ridge, to prevent accidentally bumping brow or eye with the instrument. (Some doctors advocate using this thumb to help hold the eye open, but patients hate and resist it. Have a colleague try it on you if you need convincing.) Slowly move toward the patient, slowly decreasing your diopters toward zero (increasing your focal length). In this way you focus successively on cornea, lens, vitreous, and finally retina. The appearance of black spots at any point tells you that opacities are in the path of the light and will have to be accounted for or circumvented in inspecting the retina. You should wind up with the instrument only 3 to 5 cm from the patient's eye. When you see the retina, look for the first distinct structure in the area. Sometimes this will be the optic disk, more often a vessel. Bring the structure into sharp focus by rotating (changing) your lens wheel as needed. A zero reading often works well. Myopic examiners need a negative or red number (unless the patient's refractive error balances the examiner's). Aphakic patients require a high positive, often + 10; by contrast, the patient who has an intraocular lens implant after cataract surgery has no such special need.

Now move along the vessel in the direction leading to larger caliber (i.e., toward "junctures" of vessels). Soon you will reach the optic disk. Study its color, its lateral margins, the size of the optic cup, the disk's elevation if any, and the pattern of vessels emerging from it. Record the details in a drawing if you wish to discuss abnormalities, to follow them over time, or to enhance your funduscopic technique. Try to appreciate pulsations of the retinal veins overlying the disk. This is easiest to see where an artery, or a bend in the vein, causes apparent diagonal interruption of one edge of the contained venous blood column.

Next, move out along the superior temporal artery, observing its normally slowly diminishing caliber, its crossovers of veins, any focal change in color, caliber, or content, and any abnormalities of background retina that come into view in the same fields. Move as far peripherally as possible, by directing the light in that direction. You will have to crane your own head and neck in an opposite direction, and sometimes it will feel as though you are about to twist yourself right under the table, not just 2 cm down and in! If the patient can slowly and steadily move her fixation point in the same direction that you want to go, that will bring more peripheral retina into view; a rapid or jerky movement by either patient or examiner will take the pupil out of the light path of your instrument. Recall, in asking the patient's assistance, that the patient's left and right are the opposite of your own! Now return to the disk by way of the vein, making parallel observations until the disk is reached. This procedure is repeated in the three other quadrants, and at the end one studies any areas of background retina that were not visualized earlier.

Finally the beam is directed temporally, or the patient is asked to look at the light. Unless the pupil is pharmacologically dilated, at best a fleeting glimpse of the macula may be obtained before pupilloconstriction or involuntary movement takes it out of view.

Do not let an interesting finding distract you from a fixed routine. Study the entity, then proceed. If you spot it out of sequence, such as with the first focus on the retina, leave it alone until its proper time. Examiners sometimes fear that they will lose the lesion and never find it again, but this never happens if one is relaxed, systematic